In computed tomography (CT) and fluoroscopy imaging systems, X-ray radiation spans a subject of interest, such as a human patient, and a portion of the radiation impacts a detector or a photographic plate where the image data is collected. In some X-ray systems, the photographic plate is then developed to produce an image, which may be used by a radiologist or attending physician for diagnostic purposes. In digital X-ray systems, a photodetector produces signals representative of the amount or intensity of radiation impacting discrete pixel regions of a detector surface. The signals may then be processed to generate an image that may be displayed for review. In CT systems, a detector array including a series of detector elements produces similar signals through various positions as a gantry is displaced around a patient.
In the images produced by such systems, contrast is created based upon the varying attenuation of the X-rays by the materials encountered as the X-rays penetrate the patient's tissue. Typically, materials having atoms with a greater atomic number will have a greater attenuation of X-rays. Thus, tissues such as bone may create relatively high contrast within an image compared to other tissues, such as fatty tissue. Some techniques used for CT and fluoroscopy imaging use a contrast agent to artificially create contrast within an area that would typically not have relatively high contrast, such as blood vessels. The contrast agents may include one or more atoms capable of attenuating X-rays with a relatively high degree of efficiency, such as iodine. For example, in CT angiography, a contrast agent is typically injected into the patient, followed by CT imaging. The contrast agent typically perfuses through certain tissues of the patient, and the resulting CT images contain regions of enhanced contrast corresponding to the areas that are perfused with the contrast agent.
The images produced by such systems may include data acquired at different times. As contrast agent takes time to perfuse, the contrast levels may differ during the time of each data acquisition. As a result, an image reconstructed from multiple acquisitions may include contrast banding artifacts. Such artifacts can lead to confusion for a physician and patient reviewing the final image.